1. Field of the Invention
The present invention relates to apparatus for the resistance butt welding of pipes of petroleum and gas trunk pipelines.
In the welding engineering practice, resistance butt welding apparatus are conventionally divided into the following three types:
first, the so-called external resistance butt welding apparatus (refer, e.g. to USSR Inventor's Certificates Nos. 231,041; 361,050; and 178,425) wherein all the apparatus' mechanisms are disposed outside of the pipes being joined. Such apparatus are quite effective for welding pipes of relatively small (140 to 520 mm) diameters, but unsuitable for handling medium and large diameter pipes, since in this case such apparatus become too bulky and heavy while featuring an inadequate stiffness;
second, the so-called combined resistance butt welding apparatus (refer, e.g., to USSR Inventor's Certificate No. 249,507) wherein the devices for alignment, for securing the apparatus in position inside the pipes, for upsetting and axially moving one pipe towards the other are disposed inside the pipes, whereas the welding transformer and current-feeding devices are located outside of the pipes. The combined apparatus are employed to weld medium diameter (520 to 820 mm) pipes under stationary conditions, which obviously limits their application. Besides, the arrangement of the welding apparatus' devices both inside and outside of the pipes being welded impedes the access to the joint being formed between the pipes. The apparatus are rather bulky and complex to operate;
third, the so-called internal resistance butt welding apparatus (refer to USSR Inventor's Certificate Nos. 136,487; 292,743; and 326,031), wherein all the mechanisms are disposed within the pipes to be joined. In construction of trunk pipelines when welding apparatus has to be moved along the pipeline being laid from a finished joint to the next one to be welded, the welding apparatus of the internal type is the most effective, because in operation it travels inside the pipes, which is an ideal way therefor when a pipeline is laid over an off-road terrain.
Despite the apparent advantages of the internal welding apparatus, their practical application has heretofore been limited because of the rigid requirements their construction has to meet and the complexity of their manufacture.
The present invention is specifically concerned with a pipe resistance butt welding apparatus disposable inside the pipes to be welded.
2. Description of the Prior Art
One of the earliest resistance butt welding apparatus of the internal type was that disclosed in the USSR Inventor's Certificate No. 136,487. This apparatus, intended for butt welding the ends of mainly large diameter pipes, comprises an elongated cylindrical body which carries telescopically mounted internal expanding clamp for fixing the pipes to be welded with respect to the apparatus, and cylinders. Two of the cylinders serve to actuate, i.e. to expand, the clamps and thereby to hold the apparatus in position inside the pipes being welded, and the third cylinder is intended to move one of these clamps axially when the pipes are being drawn together or upset. Like most of the internal apparatus, this apparatus has a drive and a motor to move it inside the pipes, and a welding transformer. A large diameter of the telescopic cylinders used in the above apparatus complicates both the manufacture and the operation and maintenance thereof. This in particular applies to the sealing of lengthy clearances between the cylinder and the body of the apparatus and between the annular rod and the annular cylinder body.
There is also known a pipe resistance butt welding apparatus (USSR Inventor's Certificate No. 292,743) comprising an elongated carrying body having two coaxially mounted supporting disks to which a fixed internal expanding clamp and a movable internal expanding clamp are respectively coupled, either of which expanding clamps has clamp elements to hold in position the apparatus inside the pipes being welded and is provided with its actuating cylinder, a cylinder secured directly to the respective supporting disk and serving to move the movable expanding clamp axially and to draw together the ends of the pipes, a drive to move the apparatus along the pipes being welded, and a ring welding transformer.
The carrying body is made in the form of a tube resting at its ends on static supports installed outside of the pipes. The fixed and movable expanding clamps are installed on the body; either of the clamps is essentially a collet mechanism having a set of outer segments making up a ring and interacting by their inside conical surface with the conical surface of expanding disks which are coupled with the rods of a plurality of cylinders serving to actuate the clamps. Said cylinders are radially offset from the axis of the apparatus and secured to the supporting disks fixedly installed on the body.
The cylinder for axially moving the movable expanding clamp is also radially offset and installed on the fixed disk. The rod of the cylinder passes through apertures in the fixed and movable expanding clamps and is coupled to a movable disk which acts upon the movable expanding clamp when the pipes being welded are being drawn together and upset.
Thus, the expanding (clamping) effort required to align the pipes being welded and to fix the apparatus inside these pipes is produced in the above-described apparatus by a plurality of relatively small cylinders, which solves the problem of providing a dependable sealing of the hydraulic system. At the same time, however, this construction gives rise to a difficulty in ensuring an accurate positioning of the cylinders, because an error in their positioning may cause angular misalignments and, as a consequence, a failure of the apparatus.
Also, the use of a plurality of cylinders disposed circumferentially around the axis of the apparatus, first, increases the size and complicates both the construction and operation of the apparatus and, secondly, fails to provide a concentrated axial force needed for an accurate alignment of pipes, upon which the weld quality depends.
Further, it is difficult to feed the working fluid to a plurality of cylinders disposed around and along the carrying body, and the location of the welding transformer in the zone of a joint being welded leads to a larger diametrical size of the apparatus, thereby making it unsuitable for welding medium diameter pipes.
In addition, the stiffness of the apparatus is not sufficient which is due to the fact that a long carrying body (tube) of a relatively small diameter carries essentially all the apparatus' devices. It is quite clear that an inadequate stiffness of the apparatus may eventually exert an adverse effect upon the weld quality.